Recently, numerous molecular targeted drugs that act specifically on a specific molecule have been developed for use as anticancer drugs. In particular, development has been proceeding on various antibody drugs having, as antigens, molecules specifically expressed in certain cancer cells or molecules exhibiting increased expression in cancer cells. In the development of such antibody drugs, a comparison is first made between expression of mRNA in cancer tissue collected at the time of surgery and expression of mRNA in normal tissue collected from a nearby site, molecules specifically expressed only in cancer tissue or molecules exhibiting increased expression in cancer tissue are identified, and antibodies are then prepared by using those molecules as antigens.
Colon cancer is manifest from cells of the intestinal mucosa. Cetuximab has previously been developed for use against colon cancer as an antibody drug that targets epidermal growth factor receptor (EGFR) (Non-Patent Documents 1 to 3). However, since EGFR is also expressed in normal tissue, Cetuximab also has the potential to act on normal tissue, thereby resulting in the desire to develop a molecular targeted drug that targets molecules more specifically expressed during colon cancer. With regard to this point, since there is only a small amount of mucosal tissue in which colon cancer occurs, there has been the problem of it being difficult to identify a target molecule by comparing cancerous mucosal cells and normal mucosal cells.